Einstein (17 page)

Thus he put
=
hv
, where
v
is the frequency and
h
is the constant of proportionality, which has since then been called Planck’s constant and has been found to be one of the most fundamental constants in nature. With this assumption Planck was immediately able to derive results in the theory of radiation that agreed with observations and thus removed the difficulties that had confronted the physicists in this field.

Planck thought he was only making a minor adjustment in the laws of physics in formulating his hypothesis, but Einstein realized that if this idea was developed consistently it would lead to a rupture of the framework of nineteenth-century physics so serious that a fundamental reconstruction would be necessary. For if the electron can oscillate only with certain discrete values of energy, it contradicts Newton’s laws of motion, laws which had been the bases for the whole structure of mechanistic physics.

Planck’s hypothesis dealt only with the mechanism of radiation and absorption of light and stated that these processes could take place only in definite amounts. He said nothing about the nature of light itself while it is propagated between the point of radiation and that of absorption. Einstein set out to investigate whether the energy transmitted by light retained this discrete character during its propagation or not. He once expressed this dilemma by the following comparison: “Even though beer is always sold in pint bottles, it does not follow that beer consists of indivisible pint portions.”

Retaining the analogy, if we wish to investigate whether the beer in a barrel actually consists of definite portions or not, and if so whether this portion is a pint, two pints, or ten pints, we can proceed as follows: We take a number of containers, say ten to be definite, and pour the beer from the barrel at random into these containers. We measure the amount in each container and then pour back the beer into the barrel. We repeat this process a number of times. If the beer does not come in portions, the average value of the beer poured into each container will be the same. If it consists of pint portions, there will be variations in the average values. For two pints the variations will be greater, and for ten they will be still greater. Thus by observing the distribution of beer among the ten vessels, we can tell whether the barrel of beer consists of portions and what size they are. We can realize it easily by imagining the extreme case that the whole content of the barrel is one portion.

The situation is similar in the case of radiation enclosed in a box. We can imagine this box to be divided into a number of cells of equal volume and consider the distribution of the energy of radiation in these cells. If the portions of radiation are large, the variations of energy among the cells will be large, and if they are small, these variations will be small. From the empirical law of distribution it follows that the variations in the violet light are greater than in the red light. Einstein drew the conclusions that violet light consists of a few large portions, while red light consists of many small ones. Exact calculations showed that the magnitude of the portions must be
hv
. Thus Einstein found that not only did emission and absorption of radiation take place in discrete amounts, but light itself must consist of definite portions. The name “photon” has since been given to the quantum of radiation.

To this conclusion, which Einstein derived theoretically, he was able to point out an experimental verification. It had been known for some time that when light shines on certain metals, electrons are given off. Electrons are fundamental particles in physics which carry a negative electric charge and constitute the outer portion of the atom. In 1902 the German physicist Philipp Lenard discovered a very startling result of this emission of electrons. He found that the intensity of light falling on the metal had no effect on the energy with which the electrons are ejected from the metal, but that this energy depends only on the color or frequency of the light. No matter how far the source of light is moved away from the metal, the electrons are still ejected with the same velocity, though of course the number ejected is
smaller. But when violet light is used instead of red, the velocity of the electrons is much greater.

According to Einstein’s view, the explanation is quite simple. No matter what distance light of a certain color has traveled from the source, it still consists of the same portions of energy, the only difference being that, farther away from the source, the individual portions are spread out thinner. The ejection of an electron occurs when a whole quantum of radiation is absorbed by a single electron, which then comes off with the energy of the photon. Thus the distance between the source and the metal has no effect on the energy of the single electron emitted. Furthermore, the difference between violet and red light is that a different amount of energy is possessed by the photon. Hence an electron that absorbs a violet photon naturally comes off with higher velocity than one that absorbs a red photon.

To form another analogy, let us consider the bombardment of a fortification by machine guns and by heavy artillery. Even if the total weight of projectiles fired is the same in both cases, the effects produced are of a very different character. The machine-gun bullets make a very large number of small dents, while the artillery shells make a few big holes. Moreover, the average intensity of gunfire has very little effect on the magnitude of the holes, but only on their number.

With his hypothesis on the discontinuous nature of light Einstein threw doubt on the entire conception of a continuous field of force. If light consists of photons, the electric and magnetic fields cannot fill all space continuously, and the whole of the electromagnetic theory of light based on this concept has to be re-examined. The discontinuous structure is apparently inconsistent, however, with some observed phenomena, in particular with interference and diffraction of light, which are explained so well by the theory of continuous waves. Einstein, who was well aware of this difficulty, looked upon his assumption only as a provisional hypothesis, without any lasting value. He therefore entitled the paper in which he presented his discovery: “On a Heuristic Point of View Regarding the Production and Transformation of Light.”

It is interesting to note that Einstein’s new quantum theory of light was based upon the research of two German physicists who were later to play important roles in his life. Max Planck was first to advocate the significance of Einstein’s theory of relativity, and Philipp Lenard was to oppose it most vehemently on philosophical, political, and racial grounds.

The researches whose results Einstein published at Bern in 1905 were so unusual that to the physicists of the Swiss universities they seemed incompatible with the assigned work of a minor official of the patent office. Attempts were soon made to bring Einstein to teach at the University of Zurich. At this time Professor Kleiner was the leading personality in physics there. He was a man who realized that Einstein’s papers revealed an unusual talent, but who did not really understand them. He felt it his duty to do the best for his university and endeavored to appoint Einstein professor at Zurich.

According to the regulations in force at Zurich as well as at other Germanic universities, no one could be appointed professor at a university unless he had previously been a
Privatdozent
. This is a position for which there is no analogue in the universities of western Europe and America. A young man with scientific achievements may apply for permission to teach at a university. He has no obligations and can lecture as much or as little as he desires, but receives no remuneration except the usually very small fees paid by students who attend his lectures. Since for this reason the number of
Privatdozenten
does not have to be restricted, this system has the advantage that every young scientist has an opportunity to show his teaching abilities and the universities have a large number of candidates to choose from in appointing their professors. The disadvantage, of course, is that in practice only persons with private means or another position which supports them can enter this career. With his position at the patent office, Einstein was in the latter situation.

Professor Kleiner advised him to become a
Privatdozent
at the university of Bern, so that after a short while he could then be eligible for a professorship at Zurich. Although he did not like the idea of giving regular lectures, Einstein followed the advice. Consequently his lectures were not very well prepared, and
since the students were not obliged to attend them, only a few friends came. Furthermore, Einstein was then in the midst of a veritable maelstrom of new discoveries and it was difficult to arrange his material in a way appropriate to the capacities of the average student. Professor Kleiner once came to Bern to hear Einstein lecture and afterward remarked to him that such lectures did not seem on a level fitted for the students. Einstein answered: “I don’t demand to be appointed professor at Zurich.”

At that time the professorship of theoretical physics at the University of Zurich became vacant, but the board of education of the canton of Zurich, which was in charge of the university, had its own plans for this position. The majority of the board of education belonged to the Social Democratic Party, and they had in Zurich a party comrade who appeared to be a suitable candidate, from both the political and the scientific viewpoint. This man was Friedrich Adler, Einstein’s former fellow student at the Zurich Polytechnic, who was then a
Privatdozent
at the University of Zurich. As the son of the leader of the Austrian Social Democrats, he was held in high esteem by the party members in Zurich. Friedrich Adler was a man imbued with a fanatical love of truth and was interested in physics chiefly because of its philosophical aspects. He was in every respect a man who would not shrink from uttering what he regarded as the truth even if it was to his own disadvantage. Learning that it was possible to obtain Einstein for the university, he told the board of education: “If it is possible to obtain a man like Einstein for our university, it would be absurd to appoint me. I must quite frankly say that my ability as a research physicist does not bear even the slightest comparison to Einstein’s. Such an opportunity to obtain a man who can benefit us so much by raising the general level of the university should not be lost because of political sympathies.”

So in 1909, despite the political leaning of the board of education and the leading professor’s disapproval of his mode of lecturing, Einstein was appointed professor “extraordinary” at the University of Zurich.

The call to Zurich gave Einstein for the first time a position with a certain public prestige. Most
Privatdozenten
feel that they have become important persons when they attain professorial rank, for then they can lord it over the
Dozenten
instead of being passive objects to be dealt with by the university administration. For Einstein this was naturally no cause for satisfaction. He had not suffered in any way while a
Privatdozent
, and
he did not have any desire to dominate others. Besides, he had not been anxious enough for the position to derive any great pleasure from its attainment.

From the financial point of view, the position of a professor “extraordinary” was not very lucrative. His income was no larger than it had been at the patent office and, moreover, he could no longer lead an inexpensive and pleasant bohemian life now that he had acquired a certain social status in the city. Though he kept expenses at a minimum, he had to spend money for things from which he derived no pleasure, but which were required by his social position. In order to improve the financial situation, his wife took in students to board. He once said jokingly: “In my relativity theory I set up a clock at every point in space, but in reality I find it difficult to provide even one clock in my room.”

Einstein loved the city of Zurich, which had become his home. His wife also felt more at home here than anywhere else. Collaboration with students and colleagues, which was now possible, was a great stimulus to Einstein. Administrative duties and regular teaching, however, had few attractions and in certain respects many difficulties. This was due not only to the constraint a person of such great creative ability finds himself under when required to expend his efforts on tasks that do not appear important, but also to Einstein’s paradoxical relation to society, arising from his personality.

The immediate impression that Einstein made on his environment was a conflicting one. He behaved in the same way to everybody. The tone with which he talked to the leading officials of the university was the same as that with which he spoke to his grocer or to the scrubwoman in the laboratory. As a result of his great scientific discoveries, Einstein had already acquired a profound inner feeling of security. The pressure that had often burdened his youth was gone. He now saw himself in the midst of the work to which he was going to devote his life and to which he felt himself equal. Alongside this work the problems of daily life did not appear very important. Actually he found it very difficult to take them seriously. His attitude in intercourse with other people, consequently, was on the whole one of amusement. He saw everyday matters in a somewhat comical light, and something of this attitude manifested itself in every word he spoke; his sense of humor was readily apparent. When someone said something funny, whether intentionally or not, Einstein’s response was very animated. The laughter that welled up from the very depth of his being was one of his characteristics
that immediately attracted one’s attention. To those about him his laughter was a source of joy and added to their vitality. Yet sometimes one felt that it contained an element of criticism, which was unpleasant for some. Persons who occupied an important social position frequently had no desire to belong to a world whose ridiculousness in comparison to the greater problems of nature was reflected in this laughter. But people of lesser rank were always pleased by Einstein’s personality.